U.S. patent application number 14/416410 was filed with the patent office on 2015-07-23 for alkaline earth metal silicate phosphor and method for producing same.
The applicant listed for this patent is SUMITOMO METAL MINING CO., LTD., TOHOKU UNIVERSITY. Invention is credited to Masato Kakihana, Hideki Kato, Tetsufumi Komukai, Satoko Tezuka, Jun Yokoyama.
Application Number | 20150203749 14/416410 |
Document ID | / |
Family ID | 50027696 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203749 |
Kind Code |
A1 |
Komukai; Tetsufumi ; et
al. |
July 23, 2015 |
ALKALINE EARTH METAL SILICATE PHOSPHOR AND METHOD FOR PRODUCING
SAME
Abstract
An object of the present invention is to provide: an alkaline
earth metal silicate phosphor to which Eu is added as an activator,
and which has an emission peak wavelength of 600 nm or more, high
luminance and excellent color rendering properties; and a method
for producing the alkaline earth metal silicate phosphor. An
alkaline earth metal silicate phosphor of the present invention is
represented by composition formula (1) and having an emission peak
wavelength of 600 nm or more and a circularity of 85% or more.
Composition formula (1):
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f (in the
formula, a, b, c, d, e and f satisfy 0.4<a<0.6,
0.4<b<0.6, 0.01<c<0.05, 0.01.ltoreq.d<0.4,
0.7.ltoreq.e.ltoreq.1.3, 3.0.ltoreq.f.ltoreq.5.0 and
a+b+c+d=1).
Inventors: |
Komukai; Tetsufumi; (Chiba,
JP) ; Yokoyama; Jun; (Chiba, JP) ; Kakihana;
Masato; (Miyagi, JP) ; Tezuka; Satoko;
(Miyagi, JP) ; Kato; Hideki; (Miyagi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO METAL MINING CO., LTD.
TOHOKU UNIVERSITY |
Tokyo
Sendai-shi, Miyagi |
|
JP
JP |
|
|
Family ID: |
50027696 |
Appl. No.: |
14/416410 |
Filed: |
June 17, 2013 |
PCT Filed: |
June 17, 2013 |
PCT NO: |
PCT/JP2013/066588 |
371 Date: |
January 22, 2015 |
Current U.S.
Class: |
252/301.4F |
Current CPC
Class: |
C09K 11/7734
20130101 |
International
Class: |
C09K 11/77 20060101
C09K011/77 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2012 |
JP |
2012-168795 |
Nov 28, 2012 |
JP |
2012-259996 |
Claims
1. An alkaline earth metal silicate phosphor being represented by
the following composition formula (1) and having an emission peak
wavelength of 600 nm or more and a circularity of 85% or more:
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f composition
formula (1) wherein a, b, c, d, e and f satisfy 0.4<a<0.6,
0.4<b<0.6, 0.01<c<0.05, 0.01.ltoreq.d<0.4,
0.7.ltoreq.e.ltoreq.1.3, 3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1.
2. The alkaline earth metal silicate phosphor according to claim 1,
wherein at least a part of barium (Ba) that is a component of the
alkaline earth metal silicate phosphor is derived from a flux
including barium chloride which is to be mixed at the time of
firing.
3. The alkaline earth metal silicate phosphor according to claim 1,
wherein an emission peak intensity excited at a wavelength by which
a maximum excitation intensity is obtained (I.sub.max) and an
emission peak intensity at an excitation wavelength of 550 nm
(I.sub.ex550 nm) satisfy a relationship of (I.sub.ex550
nm)/(I.sub.max)<0.25.
4. A method for producing an alkaline earth metal silicate phosphor
being represented by composition formula (1):
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f; wherein a,
b, c, d, e and f satisfy 0.4<a<0.6, 0.4<b<0.6,
0.01<c<0.05, 0.01.ltoreq.d<0.4, 0.7.ltoreq.e.ltoreq.1.3,
3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1; and having an emission peak
wavelength of 600 nm or more and a circularity of 85% or more, the
method comprising: a gel body forming step of mixing and stirring
an aqueous solution of an alkaline earth metal and an europium
compound, and an aqueous solution of a water-soluble silicon
compound to form a gel body; a drying step of drying the gel body
obtained in the gel body forming step; a calcining step of
calcining a dried matter obtained in the drying step in a
temperature condition of from 600.degree. C. to 1,400.degree. C. in
an air atmosphere; and a firing step of mixing a calcined powder
obtained in the calcining step with a flux including at least
barium chloride, followed by firing in a temperature condition of
from 1,000.degree. C. to 1,350.degree. C. under a reducing
atmosphere.
5. The method for producing an alkaline earth metal silicate
phosphor according to claim 4, wherein in the gel body forming
step, a gel body is formed by mixing and stirring at a solution
temperature of from 20.degree. C. to 100.degree. C.
6. The method for producing an alkaline earth metal silicate
phosphor according to claim 4, wherein a remaining flux is removed
from a fired product obtained in the firing step.
7. The alkaline earth metal silicate phosphor according to claim 2,
wherein an emission peak intensity excited at a wavelength by which
a maximum excitation intensity is obtained (I.sub.max) and an
emission peak intensity at an excitation wavelength of 550 nm
(I.sub.ex550 nm) satisfy a relationship of (I.sub.ex550
nm)/(I.sub.max)<0.25.
8. The method for producing an alkaline earth metal silicate
phosphor according to claim 5, wherein a remaining flux is removed
from a fired product obtained in the firing step.
Description
TECHNICAL FIELD
[0001] The present invention relates to an alkaline earth metal
silicate phosphor and a method for producing the alkaline earth
metal silicate phosphor, more specifically, relates to an alkaline
earth metal silicate phosphor suitable as a red phosphor which is
used for illumination, a display or the like, and which emits
fluorescence having a high luminance by a near ultra violet light
to a blue light, and a method for producing the alkaline earth
metal silicate phosphor. This application claims priority on the
basis of Japanese Patent Application No. 2012-168795 filed on Jul.
30, 2012, and Japanese Patent Application No. 2012-259996 filed on
Nov. 28, 2012 in Japan, which are hereby incorporated by
reference.
BACKGROUND ART
[0002] A white LED emits a white light by mixing luminescences from
a near ultra violet or blue LED and a phosphor. Conventionally,
development and research have been vigorously made of the white LED
as an LCD backlight light source for a small size portable device
or the like, while expansion to an illumination application thereof
as a next-generation application advances.
[0003] In the backlight application or the like, a so-called pseudo
white has been widely used in which a blue LED and an YAG:Ce.sup.3+
are used in combination. However, the white light obtained by this
combination has a problem that the color rendering property is low
when used for illumination due to the lack of red components. In
order to improve this point, a white LED with the use of a blue LED
along with a green or yellow phosphor and a red phosphor is
proposed. In addition, as a white LED having a higher color
rendering is also proposed a white LED with the use of a near ultra
violet to violet LED along with blue, green and red phosphors in a
combined system.
[0004] As an example of the red phosphor used for these white LEDs,
nitride phosphor such as CaAlSiN.sub.3:Eu or (Sr, Ca)AlSiN.sub.3
(e.g., refer to Patent Literature 1 or 2), or a sulfide phosphor
such as CaS:Eu, SrS:Eu or (Ca, Sr)S:Eu (e.g., refer to Patent
Literature 3) is proposed.
[0005] Although the nitride phosphor has a high performance, a
producing step is required of performing annealing at a high
temperature of around 2,000.degree. C. under a nitrogen pressurized
atmosphere, which makes the production difficult and requires a
special facility. In addition, although the sulfide phosphor is
relatively easily produced, there is a problem in that the
production involves generation of a bad smell, or corrosion of a
wiring material such as Ag or Cu caused by sulfur generated through
decomposition.
[0006] In addition, these nitride phosphor and sulfide phosphor
have an excitation spectrum extending to a long wavelength side, so
that when a white LED is prepared by mixing them with a yellow to
green phosphor, there is also a problem in that they are easy to
reabsorb light emitted from the green to yellow phosphor and then
emit light, that is, a so-called multistage excitation is easy to
occur. When such red phosphors are used and mixed with a green or
yellow phosphor and a blue excitation is made, there easily arises
unevenness in color, or deterioration of the luminous efficiency of
the white LED. In order to reduce the effect of such a multistage
excitation, a structure in which fluorescent layers are layered or
separated is proposed. However, there is a problem in that a
producing step for a white LED is complicated.
[0007] As one of phosphors other than the nitride phosphor and the
sulfide phosphor, a europium (Eu)-activated alkaline earth metal
silicate phosphor is known. For example, (Sr, Ba).sub.2SiO.sub.4:Eu
is well-known. Such an alkaline earth metal silicate phosphor is
widely used, because of the characteristics that the production is
relatively easy but does not require a special producing facility,
and adjustment of the emission wavelength is possible in accordance
with the Ba/Sr ratio.
[0008] However, in such alkaline earth metal silicate phosphors,
the one having an emission peak wavelength of more than 600 nm is
not known. A conventional alkaline earth metal silicate phosphor
has too short wavelength to be used as a red phosphor (e.g., refer
to Non Patent Literature 2).
[0009] In addition, in Patent Literature 4 is disclosed a phosphor
having a composition of (Sr.sub.x, Ba.sub.y, Ca.sub.z,
Eu.sub.w).sub.2SiO.sub.4:Eu, which emits light having a long
wavelength of 600 nm or more by a blue excitation. However, it is
defined that, in order to prevent an increase in the moisture
absorption, the adding amount of a crystal grower is restricted to
0.01% by weight or more but 0.3% by weight or less with respect to
a whole base powder. In such a case, there are problems in that not
only the crystal growth occurs insufficiently to produce a
practically sufficient luminance, but also the obtained phosphor
has a so deformed shape that, when the phosphor is mixed in resin
for the production of a white LED element, there easily arises
ununiformity or unevenness.
CITATION LIST
Patent Literature
[0010] Patent Literature 1: JP 2000-244021 A [0011] Patent
Literature 2: JP 2006-008721 A [0012] Patent Literature 3: JP
S56-82876 A [0013] Patent Literature 4: JP 2008-24791 A
Non Patent Literature
[0013] [0014] Non Patent Literature 1: Hakusyoku LED Syomei-gijutsu
No Subete (in Japanese) (Light emitting diode), Kogyo Chosakai
Publishing Co., Ltd., p 107 [0015] Non Patent Literature 2: T. L.
Barry J. Electrochem. Soc. 115 (1968) 1181-1184
SUMMARY OF INVENTION
Technical Problem
[0016] Accordingly, the present invention has been proposed in view
of such actual circumstances, and has as an object to provide an
alkaline earth metal silicate phosphor to which Eu is added as an
activator, and which has an emission peak wavelength of 600 nm or
more, a high circularity of particle, a high luminance and an
excellent color rendering property, and a method for producing the
alkaline earth metal silicate phosphor.
Solution to Problem
[0017] As a result of intensive studies made by the present
inventors to solve the above described problems, it has been found
that an alkaline earth metal silicate phosphor composed of a
predetermined composition obtained by performing a firing process
in the presence of a flux including at least barium chloride
(BaCl.sub.2) has an emission peak wavelength of more than 600 nm, a
high circularity of particle suitable for a white LED, and a higher
fluorescent luminance than that of a conventional phosphor, and
thus the present invention has been achieved.
[0018] That is, according to the present invention, an alkaline
earth metal silicate phosphor is represented by the following
composition formula (1) and has an emission peak wavelength of 600
nm or more and a circularity of particle of 85% or more.
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f Composition
formula (1)
[0019] (in the formula, a, b, c, d, e and f satisfy
0.4<a<0.6, 0.4<b<0.6, 0.01<c<0.05,
0.01.ltoreq.d<0.4, 0.7.ltoreq.e.ltoreq.1.3,
3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1).
[0020] Herein, at least a part of barium (Ba) that is a component
of the alkaline earth metal silicate phosphor is derived from a
flux including barium chloride which is to be mixed at the time of
firing.
[0021] In addition, an emission peak intensity excited at a
wavelength by which the maximum excitation intensity is obtained
(I.sub.max) and an emission peak intensity at an excitation
wavelength of 550 nm (I.sub.ex550 nm) are satisfying a relationship
of (I.sub.ex550 nm)/(I.sub.max)<0.25.
[0022] In addition, according to the present invention, a method
for producing an alkaline earth metal silicate phosphor is
represented by composition formula (1):
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f; wherein a,
b, c, d, e and f satisfy 0.4<a<0.6, 0.4<b<0.6,
0.01<c<0.05, 0.01.ltoreq.d<0.4, 0.7.ltoreq.e.ltoreq.1.3,
3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1; and has an emission peak
wavelength of 600 nm or more and a circularity of particle of 85%
or more, the method includes: a gel body forming step of mixing and
stirring an aqueous solution of an alkaline earth metal and an
europium compound, and an aqueous solution of a water-soluble
silicon compound to form a gel body; a drying step of drying the
gel body obtained in the gel body forming step; a calcining step of
calcining a dried matter obtained in the drying step in a
temperature condition of from 600.degree. C. to 1,400.degree. C. in
an air atmosphere; and a firing step of mixing a calcined powder
obtained in the calcining step with a flux including at least
barium chloride, followed by firing in a temperature condition of
from 1,000.degree. C. to 1,350.degree. C. under a reducing
atmosphere.
[0023] Herein, in the above described gel body forming step, it is
preferable to perform the mixing and stirring at a solution
temperature of from 20.degree. C. to 100.degree. C. in order to
form the gel body.
[0024] In addition, it is preferable to remove the remaining flux
from the fired product obtained in the above described firing
step.
Advantageous Effects of Invention
[0025] According to the present invention, the phosphor has an
emission peak wavelength of 600 nm or more, a high circularity of
particle, an excellent dispersibility, and a higher luminance and a
more excellent color rendering property than those of a
conventional phosphor, so that the phosphor may be suitably used as
a red phosphor for the production of a white LED.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 illustrates excitation emission spectra of
CaAlSiN.sub.3:Eu and (Sr, Ca)AlSiN.sub.3:Eu which have been
conventionally used as a red phosphor.
[0027] FIG. 2 illustrates emission spectra of the phosphors
prepared in Examples 1 to 3.
[0028] FIG. 3 is electron microscopy (SEM) images of the phosphor
particles prepared in Example 1.
[0029] FIG. 4 illustrates emission spectra of the phosphors
prepared in Comparative Examples 1, 2 and 4.
[0030] FIG. 5 is electron microscopy (SEM) images of the phosphor
particles prepared in Comparative Example 4.
DESCRIPTION OF EMBODIMENTS
[0031] Hereinafter, a detailed description is made of a specific
embodiment (hereinafter, referred to as "the embodiment") of the
alkaline earth metal silicate phosphor according to the present
invention and a method for producing the alkaline earth metal
silicate phosphor in the following order. Note that the present
invention is not limited to the following embodiment, and various
kinds of modifications are possible without deviating from the
scope of the present invention.
[0032] 1. An alkaline earth metal silicate phosphor
[0033] 2. A method for producing the alkaline earth metal silicate
phosphor
[0034] 2-1. A step of forming a gel body
[0035] 2-2. A step of performing drying
[0036] 2-3. A step of performing calcining
[0037] 2-4. A step of performing firing
[0038] 3. Examples
1. AN ALKALINE EARTH METAL SILICATE PHOSPHOR
[0039] The alkaline earth metal silicate phosphor according to the
embodiment is a complex oxide to which europium (Eu) of rare earth
elements is added as an activator, represented by composition
formula (1) as described below, and having an emission peak
wavelength of 600 nm or more and a circularity of particle of 85%
or more.
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f Composition
formula (1)
[0040] (in the above described formula, a, b, c, d, e and f
satisfying 0.4<a<0.6, 0.4<b<0.6, 0.01<c<0.05,
0.01.ltoreq.d<0.4, 0.7.ltoreq.e.ltoreq.1.3,
3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1).
[0041] Specifically, in this alkaline earth metal silicate
phosphor, the mixing ratio of strontium (Sr) and calcium (Ca) of
alkaline earth metals is defined for the numbers (a) and (b) of
atom so as to be 0.4<a<0.6 and 0.4<b<0.6, respectively.
Because the ratio of these alkaline earth metals (a, b) is more
than 0.4 but less than 0.6, the percentage of a crystal phase
exhibiting a luminescence of 600 nm or more relatively increases,
so that the phosphor has an emission peak wavelength of 600 nm or
more.
[0042] In addition, in this alkaline earth metal silicate phosphor,
the mixing ratio of barium (Ba) of alkaline earth metals is defined
for the number (c) of atom so as to be 0.01<c<0.05. In
addition to the above described Sr and Ca, containing Ba of
alkaline earth metals in the ratio of 0.01<c<0.05 allows the
peak intensity of the emission peak at 600 nm or more to be
enhanced, so that the phosphor has an extremely high light emission
luminance.
[0043] At least a part of Ba that is a component of this alkaline
earth metal silicate phosphor is derived from a flux including
barium chloride (BaCl.sub.2) which is to be mixed at the time of
firing in the phosphor production. Although a detailed description
is made in the following description of a producing method, using a
flux including at least BaCl.sub.2 at the time of firing allows
doping with Ba as a component, thereby enhancing the light emission
luminance of the obtained phosphor.
[0044] In addition, the ratio of europium (Eu) added as an
activator is defined for the number (d) of atom so as to be
0.01.ltoreq.d<0.4. Containing Eu as an activator in the ratio of
0.01.ltoreq.d<0.4 allows the phosphor to emit light at a
wavelength of 600 nm or more without causing the concentration
quenching.
[0045] In addition, in this alkaline earth metal silicate phosphor,
the mixing ratio of silicon (Si) is defined for the number (e) of
atom so as to be 0.7.ltoreq.e.ltoreq.1.3. A mixing ratio of silicon
of less than 0.7 is unpreferable, because SrO, CaO,
Sr.sub.3SiO.sub.5 or Ca.sub.3SiO.sub.5, or the solid solution phase
thereof is formed, so that the crystallizability worsens and the
light emission luminance decreases. On the other hand, a mixing
ratio of silicon of more than 1.3 is also unpreferable, because
SrSiO.sub.3 or CaSiO.sub.3, or the solid solution phase thereof is
formed, so that the crystallizability worsens and the light
emission luminance decreases.
[0046] In addition, in the alkaline earth metal silicate phosphor,
the mixing ratio of oxygen (O) is defined for the number (f) of
atom so as to be 3.0.ltoreq.f.ltoreq.5.0. When the mixing ratio of
oxygen is less than 3.0, oxygen defect or substitution amount of O
with Cl or the like is considered to be so excessive that the light
emission property remarkably worsens. On the other hand, when the
mixing ratio of oxygen is more than 5.0, unreduced Eu.sub.2O.sub.3
or a surface-adsorbed component is considered to be so excessive
that the light emission property remarkably worsens similarly.
Accordingly, in the alkaline earth metal silicate phosphor
according to the embodiment, the ratio of oxygen (f) is defined so
as to be 3.0.ltoreq.f.ltoreq.5.0.
[0047] Note that it is considered that the coupling ratio of each
of the above described constituent elements of Sr, Ca, Ba and Eu to
oxygen is 1:1 (SrO, CaO, BaO, EuO), and that of Si to oxygen is 1:2
(SiO.sub.2) in general. In this case, e=0.7 results in f=3.4, and
e=1.3 results in f=4.6, so that the range of the amount of oxygen
is unambiguously 3.4.ltoreq.f.ltoreq.4.6. However, due to the
presence of oxygen defect in the crystal or doping with Cl
(substitution of the O site) of for example a flux component, the
value may have f<3.4, Eu.sub.2O.sub.3 used as a europium
compound for example may remain in a partly unreduced state, or due
to the presence of a surface-adsorbed component or the like, the
value may have f>4.6.
[0048] In accordance with the alkaline earth metal silicate
phosphor having the above described composition, because of an
emission peak wavelength of 600 nm or more, or a high circularity
of particle, the light emission luminance is extremely higher than
that of a conventional phosphor, so that the phosphor may be
suitably used as a red phosphor. In addition, such a phosphor has a
high absorbing ratio of an excitation light, so that the phosphor
is excellent in light emission property.
[0049] Herein, the circularity is a ratio of the diameter
equivalent to a circle area with respect to the diameter equivalent
to a circle for the circumference length in a projection drawing of
the particle, so the circularity of a monodispersed and completely
spherical particle is 100%. The phosphor is more advantageous in
emission intensity and dispersibility as the sphere property is
higher. The above described alkaline earth metal silicate phosphor
has a high circularity of particle of 85% or more. Also in this
point, for example, in the production of a white LED, the phosphor
may be kneaded into resin together with a yellow or green phosphor
or the like so as to exhibit a high dispersibility, so that a white
LED excellent in light emission property may be produced.
[0050] In addition, in this alkaline earth metal silicate phosphor,
when an emission peak intensity excited at a wavelength by which
the maximum excitation intensity is obtained is regarded as
I.sub.max, and an emission peak intensity at an excitation
wavelength of 550 nm is regarded as I.sub.ex550 nm, a relationship
of (I.sub.ex550 nm)/(I.sub.max)<0.25 is satisfied.
[0051] Herein, in FIG. 1 are indicated excitation emission spectra
of CaAlSiN.sub.3:Eu (hereinafter, also referred to as "CASN") and
(Sr, Ca)AlSiN.sub.3:Eu (hereinafter, also referred to as "SCASN")
which have been conventionally used as a red phosphor (refer to Non
Patent Literature 1). Note that the excitation intensity
corresponds to an emission intensity excited at each wavelength. As
indicated in FIG. 1, the excitation spectra of both of the CASN and
SCASN extend to a long wavelength side of a green to yellow region,
and for example, the emission intensity (I.sub.ex550 nm) at 550 nm
excitation is more than 50% of the emission intensity (I.sub.max)
at 400 nm excitation (the wavelength by which the maximum
excitation intensity is obtained) ((I.sub.ex550
nm)/(I.sub.max)>0.5). This indicates that when a white LED is
produced by mixing these red phosphors with a green to yellow
phosphor for example, the red phosphors reabsorb light emitted from
the green to yellow phosphor, thereby being excited to emit a red
light. In other words, this indicates that a multistage excitation
is easy to occur. When such a red phosphor is used for the
preparation of a white LED, there easily arises unevenness in
color, or deterioration of the luminous efficiency.
[0052] In contrast, in the alkaline earth metal silicate phosphor
according to the embodiment, a relationship of (I.sub.ex550
nm)/(I.sub.max)<0.25 is satisfied, as described above. Because
the alkaline earth metal silicate phosphor has such an excitation
spectrum shape, even when being mixed for use with a green or
yellow phosphor, a multistage excitation is suppressed, for example
deviation or unevenness in color of a white LED, decrease of the
efficiency or color shift due to a multistage excitation may be
suppressed. Accordingly, the phosphor exhibits an extremely high
color purity and has an excellent color rendering property.
2. A METHOD FOR PRODUCING THE ALKALINE EARTH METAL SILICATE
PHOSPHOR
[0053] Next, a description is made of a method for producing the
alkaline earth metal silicate phosphor composed of the above
described characteristic composition.
[0054] A method for producing the alkaline earth metal silicate
phosphor according to the embodiment includes a gel body forming
step of mixing and stirring an aqueous solution of a raw material
metal and an aqueous solution of a water-soluble silicon compound
to form a gel body, a drying step of drying the gel body, a
calcining step of calcining the dried matter, and a firing step of
mixing the calcined powder with a flux and reduction firing the
mixture. Hereinafter, a detailed description is made of each of the
steps.
<2-1. A Step of Forming a Gel Body>
[0055] In a step of forming a gel body, salts of raw material
metals and a compound of europium (Eu) as an activator weighted in
a predetermined ratio are dissolved to form an aqueous solution. In
the obtained aqueous solution, a predetermined amount of an aqueous
solution of a water-soluble silicon compound is added, and the
mixture is stirred, so that a gel body is obtained.
[0056] In this way, mixing raw material metals with a water-soluble
silicon compound so as to form a gel body allows the raw material
to be uniformly dispersed, so that a phosphor in which the
components composed of the raw material metals are uniformly
distributed may be obtained. Accordingly, the phosphor has a higher
light emission luminance.
[0057] Specifically, first of all, raw material metal salts and an
Eu compound added as an activator weighted in a predetermined ratio
are mixed, so that an aqueous solution is prepared.
[0058] As a raw material metal salt, at least a calcium (Ca) salt,
a strontium (Sr) salt and a europium (Eu) compound are used. As an
example of the calcium salt and the strontium salt, a carbonate,
acetate, nitrate, chloride salt or the like may be used, and among
them, carbonate and acetate salts are preferably used. In addition,
as a europium compound added as an activator, an oxide, acetate
salt, nitrate salt or the like may be used, or simple europium may
be used.
[0059] In addition, in the firing step as described below, using a
flux including at least barium chloride (BaCl.sub.2) may allow
doping with barium (Ba) that is a component of the phosphor during
the reduction firing, resulting in substitution of Sr or Ca, and
additionally, in the gel body forming step, barium (Ba) in the form
of for example a carbonate salt may be added together with the
above mentioned calcium salt, strontium salt or the like.
[0060] Note that for the purpose of improving the characteristic, a
very small amount of a rare earth element other than Eu may be
added. In this case, various kinds of rare earth elements in the
form of an oxide, chloride, nitrate salt, carbonate salt, acetate
salt or the like may be used.
[0061] The above described raw material metal salt and europium
compound are prepared as an aqueous solution (aqueous dispersion)
in which these raw materials are dispersed, and which is produced
by, first of all, adding at least the calcium salt and the
strontium salt, along with the europium compound that is an
activator in water, followed by stirring. Note that using an
organic acid such as citric acid so as to dissolve the raw
materials may produce the aqueous solution, but in this case, a
thermolysis process or the like is required to remove the organic
component within the obtained gel body.
[0062] On the other hand, in the gel body forming step, the aqueous
dispersion in which the above described raw material metal salts
are dispersed is prepared, along with a water-soluble silicon
compound (WSS) is prepared. The water-soluble silicon compound may
be prepared by, for example, adding tetraethoxysilane (TEOS) and a
dihydric alcohol as raw materials individually so as to be 1:3 or
more for the mole ratio, followed by mixing at 80.degree. C. for 1
hour, and adding in the mixture a small amount (around 0.2% of the
mixture) of acid as a catalyst, followed by stirring for 1
hour.
[0063] Using the water-soluble silicon compound prepared in this
way allows easily mixing with the aqueous dispersion in which the
raw material metal salts are dissolved. Moreover, forming a
phosphor precursor (a dry matter of the gel body) through a wet
synthesis with the use of such an aqueous solution allows a
phosphor precursor in which the raw materials are uniformly
dispersed to be obtained, in particular Eu that is an activator to
be uniformly added, so that a phosphor having a high luminance may
be effectively prepared.
[0064] As the dihydric alcohol, for example propylene glycol may be
used, and as the acid used as a catalyst, hydrochloric acid or
lactic acid may be used.
[0065] In addition, as to the water-soluble silicon compound, for
example adding TEOS and propylene glycol so as to be 1:3 or more
for the mole ratio results in the water-soluble one. When the mole
ratio is less than 1:4, it is easy to gelate. Accordingly, in the
case of preservation for a long time, TEOS and propylene glycol are
preferably mixed so as to be 1:4 or more for the mole ratio.
[0066] In the gel body forming step, the separately prepared
aqueous dispersion in which the raw material metals are dispersed
and water-soluble silicon compound, as described above, are mixed
so as to be in a desired composition ratio, so that the gel body is
prepared.
[0067] In the embodiment, the prepared alkaline earth metal
silicate phosphor is represented by composition formula (1):
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f, in formula
(1), a, b, c, d, e and f satisfying 0.4<a<0.6,
0.4<b<0.6, 0.01<c<0.05, 0.01.ltoreq.d<0.4,
0.7.ltoreq.e.ltoreq.1.3, 3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1.
Because the atom ratio in the supplied raw materials and the atomic
composition ratio of the obtained phosphor substantially match with
each other, it is preferable to weight and mix the aqueous
dispersion composed of the raw material metal salts and the Eu
compound weighted, and the water-soluble silicon compound
separately, so as to be in a desired raw material blending
ratio.
[0068] Note that Ba composes the alkaline earth metal silicate
phosphor, in which a part of Sr or Ca has been substituted and
doped with Ba included in a flux added in the firing step as
described below. Accordingly, in the firing step as described
below, it is preferable to add and mix a flux such that Ba derived
from the flux is contained in a desired composition ratio. In
addition, because the substitution with Ba derived from the flux
slightly decreases the containing percentage of Sr or Ca, it is
preferable that a first raw material blending ratio be set and then
the raw materials be weighted and mixed so as to result in the
phosphor represented by the desired composition formula.
[0069] In the formation of the gel body, in the aqueous solution in
which the alkaline earth metals are dissolved, the water-soluble
silicon compound is added and mixed, followed by stirring to
gelate. The time required for the gelation varies depending on the
type of the alkaline earth metal elements or the water content in
the aqueous solution. In addition, in order to more effectively
promote the gelation, in the water-soluble silicon compound to be
used, propylene glycol that is dihydric alcohol may be add in an
amount corresponding to 6 times to 12 times the total number of
moles of the metallic elements.
[0070] In addition, as to the gelation temperature, the solution
temperature is preferably adjusted to 20.degree. C. to 100.degree.
C., more preferably adjusted to 20.degree. C. to 80.degree. C. When
the temperature is lower than 20.degree. C., the gelation time gets
longer, but when the temperature is higher than 100.degree. C.,
water boils, which makes the uniform gelation difficult.
Accordingly, mixing and stirring the solution at a temperature of
from 20.degree. C. to 100.degree. C. allow the gel body to be
effectively formed in which the raw materials are uniformly
dispersed.
<2-2. A Step of Performing Drying>
[0071] In a drying step, the gel body obtained through the gel body
forming step is dried by, for example placing the gel body in a hot
air drier or the like.
[0072] In the gel body obtained through the gel body forming step,
as solvent components, in addition to water, a part of dihydric
alcohol such as ethanol or propylene glycol derived from the
water-soluble silicon compound (WSS) is included. Accordingly, in
this drying step, the obtained gel body is dried, so that the
solvent component included within the gel body is removed.
Accordingly, a phosphor precursor that is a dry matter of the gel
body is formed.
[0073] The drying temperature in the drying step is not limited in
particular, but it is preferable to perform drying at around
80.degree. C. to 100.degree. C. In addition, the drying time is
also not limited in particular, but may be set to around 5 hours to
10 hours.
<2-3. A Step of Performing Calcining>
[0074] In a calcining step, the phosphor precursor that is a dry
matter of the gel body obtained through the drying step is calcined
in a predetermined calcining condition, so that a calcined powder
is obtained. In this calcining step, dihydric alcohol or the like
derived from the WSS remaining after the above described drying
step is decomposed and removed, along with the carbonate salt in
the dry matter is decomposed, so that a host crystal is grown.
[0075] As the calcining process condition, the temperature
condition is preferably adjusted to 600.degree. C. to 1,400.degree.
C. in an air atmosphere. When the calcining temperature is lower
than 600.degree. C., there may arise insufficient decomposition of
the dihydric alcohol such as propylene glycol or the carbonate
salt, and insufficient growth of the host crystal. On the other
hand, a temperature of higher than 1,400.degree. C. is
unpreferable, because there arises complete sintering or byproduct
formation.
<2-4. A Step of Performing Firing>
[0076] In a firing step, the calcined powder obtained in the
calcining step is fired to be reduced in a predetermined firing
condition under a reducing atmosphere. In this firing step, the
host crystal is grown, along with the valence of Eu that is an
activator is changed from 3 to 2 so as to allow doping.
[0077] Moreover, in this firing step, it becomes important to mix
and fire the calcined powder with a flux. In particular, this
firing step is performing reduction firing in the presence of a
flux including at least barium chloride (BaCl.sub.2).
[0078] Mixing the calcined powder with a flux and performing
reduction firing allow the crystal growth to be promoted by the
presence of the flux. In addition, phosphor particles obtained by
performing reduction firing in the presence of the flux in this way
are in the order of several 10 .mu.m, are nearly monodispersed, and
have a high circularity of particle. Accordingly, for example in
the production of a white LED, when the phosphor particles are
kneaded into resin together with a green or yellow phosphor, they
may be dispersed so well that the kneading property is improved.
Note that the particle diameter of the phosphor particles may be
changed within a range of from several .mu.m to 50 .mu.m in
accordance with the type or adding amount of the flux, or the
firing temperature.
[0079] Moreover, in particular using as a flux the one including at
least BaCl.sub.2 allows a phosphor having a higher luminance than
that of a conventional phosphor to be obtained. In this regard, the
mechanism is not sure, but it is considered that using a flux
including BaCl.sub.2 allows doping with Ba included in the flux as
a component of the phosphor, thereby improving the light emission
luminance.
[0080] The flux to be mixed with the calcined powder is defined as
a flux including at least barium chloride (BaCl.sub.2) as described
above. In other words, a flux including BaCl.sub.2 alone, or along
with BaCl.sub.2 one or more compounds such as a chloride (such as
NH.sub.4Cl, LiCl, NaCl, KCl, CsCl, CaCl.sub.2, SrCl.sub.2,
YCl.sub.3, ZnCl.sub.2, MgCl.sub.2 or RbCl) or a hydrate salt
thereof, a fluoride (such as LiF, NaF, KF, CsF, CaF.sub.2,
BaF.sub.2, SrF.sub.2, AlF.sub.3, MgF.sub.2 or YF.sub.3), or a
phosphate salt (such as K.sub.3PO.sub.4, K.sub.2HPO.sub.4,
KH.sub.2PO.sub.4, Na.sub.3PO.sub.4, Na.sub.2HPO.sub.4,
NaH.sub.2PO.sub.4, Li.sub.3PO.sub.4, Li.sub.2HPO.sub.4,
LiH.sub.2PO.sub.4, (NH.sub.4).sub.3PO.sub.4,
(NH.sub.4).sub.2HPO.sub.4 or (NH.sub.4)H.sub.2PO.sub.4) may be
used. Among them, a flux including SrCl.sub.2 or CaCl.sub.2 along
with BaCl.sub.2 is preferably used.
[0081] In the reduction firing, as to the reducing atmosphere, a
mixed gas of a hydrogen gas and an inert gas such as a nitrogen gas
or argon gas, or the like is preferably used.
[0082] In addition, as to the temperature condition for the
reduction firing, a temperature of 1,000.degree. C. to
1,350.degree. C. is preferable, or a temperature of 1,100.degree.
C. to 1,300.degree. C. is more preferable. When the reduction
firing temperature is lower than 1,000.degree. C., the reduction
firing process applied to the calcined powder is not effectively
progressed. On the other hand, a reduction firing temperature of
higher than 1,350.degree. C. is unpreferable, because the particle
diameter becomes so enlarged that the use as a phosphor for an LED
or the like is difficult, the high temperature phase is formed as
an impurity phase, or a localized meltdown is caused.
[0083] In addition, the reduction firing processing time is
preferably from 0.5 hour to 12 hours, or more preferably from 1
hour to 6 hours. Note that the reduction firing process may be
repeatedly performed over a plurality of times.
[0084] Crushing the fired product obtained by reduction firing the
calcined powder as described above allows phosphor particles having
a desired composition to be obtained. At this time, on the surface
of the fired product (the phosphor particles), the flux mixed in
the firing step may remain. The remaining flux on the surface of
the phosphor particles is unpreferable, because deterioration of
the fluorescence intensity may be caused. Accordingly, the fired
product obtained as described above is preferably washed with water
or the like before or after the crushing, so as to remove the flux
remaining on the particle surface. After the washing process is
performed in this way, substitution with ethanol or the like and
drying are performed, so that a phosphor is obtained. Furthermore,
for the purpose of recovering the surface damage caused by the
cracking or washing in order to further improve the light emission
luminance, annealing may be performed in an appropriate atmosphere
or at an appropriate temperature.
[0085] Note that, in general, an alkaline earth metal silicate
phosphor has a problem associated with the resistance against
humidity. Accordingly, in order to improve the surface stability of
the phosphor, it is preferable to perform a surface processing for
coating the surface of the obtained phosphor particles with a
different substance. An example of the material for the surface
processing may include an organic compound, an inorganic compound,
a glass material and the like. Among them, silicon oxide that is an
oxide is preferably used in performing the surface processing.
[0086] In accordance with the producing method as described above
in detail, the alkaline earth metal silicate phosphor represented
by the composition formula of
(Sr.sub.aCa.sub.bBa.sub.cEu.sub.d).sub.2Si.sub.eO.sub.f may be
produced, in the composition formula, a, b, c, d, e and f
satisfying 0.4<a<0.6, 0.4<b<0.6, 0.01<c<0.05,
0.01.ltoreq.d<0.4, 0.7.ltoreq.e.ltoreq.1.3,
3.0.ltoreq.f.ltoreq.5.0 and a+b+c+d=1.
[0087] Moreover, the alkaline earth metal silicate phosphor
produced in this way has an emission peak wavelength of 600 nm or
more, and furthermore may emit light having a higher luminance than
that of a conventional phosphor. Accordingly, the phosphor may be
suitably used as a red phosphor. In addition, such a phosphor has a
high absorbing ratio of an excitation light, so that the phosphor
is excellent in light emission property.
[0088] In addition, in the alkaline earth metal silicate phosphor
produced in this way, from the excitation spectrum shape, in the
case of being mixed for use with a green or yellow phosphor or the
like, a multistage excitation hardly occurs, deviation or
unevenness in color of a white LED, decrease of the efficiency or
color shift due to a multistage excitation may be suppressed.
Accordingly, the phosphor may be suitably used as a red phosphor
for a white LED.
[0089] Furthermore, as can be seen from the producing method as
described above, the production may be inexpensively and easily
achieved without subjecting a complicated producing step, and
without using a special producing facility, like a conventional
nitride phosphor or sulfide phosphor.
[0090] Still further, as described above, growing the grain with
the use of a flux allows nearly monodispersed particles having a
high circularity to be obtained. Specifically, particles having a
circularity of 85% or more may be obtained. Accordingly, for
example, in the production of a white LED, when the particles are
kneaded into resin together with a yellow or green phosphor or the
like, they exhibit an excellent dispersibility.
[0091] In addition, the alkaline earth metal silicate phosphor
produced in this way is suitable for a white LED from the points of
view of the specific gravity and shape. In other words, a common
green or yellow phosphor that is used with a red phosphor in the
production of a white LED, (Ba, Sr).sub.2SiO.sub.4:Eu, (Y,
Gd)Al.sub.5O.sub.12:Ce or the like, has a specific gravity of
around 4 to 5 g/cm.sup.3, a shape such that the order is
approximately from several .mu.m to 30 .mu.m and the flattening is
small, and is nearly monodispersed, although it depends on the
composition. In contrast, CASN that is a conventional red phosphor
has a specific gravity of around 3.3 g/cm.sup.3, is an aggregate of
particles having a particle diameter of several .mu.m or less, and
has a large difference of the specific gravity or the shape with
respect to that of a green or yellow phosphor to be combined,
although it depends on the composition.
[0092] On the other hand, the specific gravity of the alkaline
earth metal silicate phosphor according to the embodiment is
assumed to be around 4 g/cm.sup.3 from the crystal data of
SrCaSiO.sub.4, so that flux firing may result in nearly
monodispersed particles growing up to several .mu.m to several 10
.mu.m and having a small flattening. Accordingly, the difference of
the specific gravity or the shape with respect to that of a common
green or yellow phosphor to be combined becomes relatively small.
The small difference of the specific gravity or the shape is very
effective in the uniform kneading with a green or yellow
phosphor.
[0093] In this way, with the use of the alkaline earth metal
silicate phosphor according to the embodiment, mixing with a
phosphor emitting a green to yellow light to form a fluorescent
layer and combining the fluorescent layer with a blue LED allow a
red component to be more effectively supplemented, so that a white
LED more excellent in color rendering property may be inexpensively
obtained.
[0094] Herein, in the preparation of a white LED, the structure is
not limited in particular, but, for example, such a structure that
the fluorescent layer is formed directly above a blue LED and is
sealed with the blue LED, or a so-called remote phosphor in which a
phosphor sheet formed of resin, rubber or the like is placed apart
from a blue LED may be used to achieve a white LED device.
[0095] Note that the green to yellow phosphor includes various
kinds of substances such as SrAl.sub.2O.sub.4:Eu,
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce, CaSc.sub.2O.sub.4:Ce, (Ba,
Sr).sub.2SiO.sub.4:Eu, Ba.sub.3Si.sub.6O.sub.12N.sub.2:Eu,
.beta.-sialon, Y.sub.3Al.sub.5O.sub.12:Ce, Y.sub.3(Al,
Ga).sub.5O.sub.12Ce, (Y, Gd).sub.3Al.sub.5O.sub.12:Eu,
Lu.sub.3Al.sub.5O.sub.12, or Ca-.alpha. sialon. Among them, in
particular, any of (Ba, Sr).sub.2SiO.sub.4:Eu,
Y.sub.3Al.sub.5O.sub.12:Ce, Y.sub.3(Al, Ga).sub.5O.sub.12:Ce, (Y,
Gd).sub.3Al.sub.5O.sub.12:Eu, Lu.sub.3Al.sub.5O.sub.12 and
Ca-.alpha. sialon is preferable.
EXAMPLES
3. EXAMPLE
[0096] Hereinafter, a more detailed description is made with
reference to Examples in which the present invention is applied.
Note that the present invention is not limited to the following
Examples.
[0097] In the Examples, a phosphor prepared in each of the Examples
and Comparative Examples was subjected to measurement of an
emission spectrum by an excitation at 455 nm, and further subjected
to measurement of an excitation spectrum with respect to the
emission peak wavelength, with the use of a fluorescence
spectrophotometer FP-6500 (made by JASCO Corporation). The emission
intensity was evaluated as a relative luminance that was
standardized by regarding the highest luminance of a conventional
yellow phosphor YAG:Ce (made by PhosphorTech Corporation,
QMK58/F-U1) as 1.
[0098] In addition, as to the luminous efficiency of the phosphor,
the absorbing ratio by the phosphor of an excitation light (the
absorbing efficiency of an excitation light) at 455 nm, internal
quantum efficiency and external quantum efficiency were measured
with the use of an integrating sphere. Note that the internal
quantum efficiency indicates a converting efficiency of an absorbed
excitation light into fluorescence. On the other hand, the external
quantum efficiency indicates a converting efficiency of an
excitation light with which the phosphor has been irradiated into
fluorescence. The external quantum efficiency is calculated by
multiplying the absorbing ratio by the internal quantum
efficiency.
[0099] Furthermore, with the use of a vacuum dispersion particle
image analyzer for particle size distribution (VD-400nano) made by
JASCO International Co., Ltd., the circularity of obtained phosphor
particles was evaluated.
Example 1
<Preparation of the Phosphor>
[0100] In Example 1, as described below, in accordance with a
solution method with the use of a water-soluble silicon compound
(WSS), a precursor was obtained, and the precursor was fired, so
that the phosphor was prepared. Note that the used WSS was prepared
by weighting tetraethoxysilane (TEOS) and propylene glycol so as to
be 1:4 for the mole ratio, followed by mixing at 80.degree. C. for
1 hour, and adding to the obtained mixture a very small amount of
lactic acid as an acid, followed by stirring for additional 1 hour.
Moreover, to this was added pure water, so that an aqueous solution
including 2 mol/L WSS was obtained.
(A Step of Forming a Gel Body)
[0101] As raw materials, CaCO.sub.3 (made by Wako Pure Chemical
Industries, Ltd.), SrCO.sub.3 (made by Kanto Chemical Co., Inc.)
and Eu.sub.2O.sub.3 (3N, made by Kojundo Chemical Lab. Co., Ltd.)
were weighted so as to have a composition formula
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4), and added in 3.5
times weight of water with respect to the total weight of the
weighted raw materials, followed by stirring at a room temperature
for 30 minutes, so that an aqueous dispersion was prepared.
Subsequently, a predetermined amount of the aqueous solution having
a concentration of 2 mol/L WSS was weighted. Next, in the aqueous
dispersion of the raw materials, the WSS aqueous solution was
added, followed by stirring at a room temperature for 10 minutes.
After the whole solution was confirmed to be in a uniform slurry
state, warming was started by a hot magnetic stirrer. The heating
temperature was set such that the mixture temperature was at
50.degree. C. Approximately 20 minutes from the start of the
warming, the whole mixture gelated, so that a uniform gel body was
obtained.
(A Step of Performing Drying)
[0102] Next, the obtained gel body was dried for 6 hours in a hot
air drier set to be 100.degree. C. The dried gel body was taken out
and then lightly crushed in a mortar, so that a phosphor precursor
that was the dry matter was obtained.
(A Step of Performing Calcining)
[0103] Next, the obtained phosphor precursor that was the dry
matter was placed in a container made of alumina, and then
subjected to a heat treatment in a temperature condition of
1,000.degree. C. in an air atmosphere for 3 hours, so that the
phosphor precursor was calcined.
(A Step of Performing Firing)
[0104] Next, to an obtained calcined powder, 20% by weight of
BaCl.sub.2 as a flux with respect to the weight of the calcined
powder were added, followed by mixing. Moreover, the mixed powder
was placed in a boat made of carbon, and then reduction fired in an
atmosphere of Ar-4% H.sub.2 in a temperature condition of
1,200.degree. C. for 4 hours with the use of an electric tubular
furnace (made by Yamada Denki Co., Ltd., TSR-630), so that a fired
product was obtained.
(A Step of Removing a Remaining Flux)
[0105] Note that the obtained fired product was crushed in an agate
mortar, the surface on which the flux component remained was washed
with the use of pure water, and then substitution with ethanol and
warm air-drying were performed, so that a phosphor was
obtained.
[0106] The finally obtained phosphor was analyzed and found to have
a composition of
Ca.sub.0.918Sr.sub.0.867Ba.sub.0.074Eu.sub.0.141SiO.sub.4. From the
composition formula, it is supposed that a part of Ca and Sr was
substituted with Ba derived from BaCl.sub.2 added as a flux. In
addition, the phosphor had a particle shape such that the particles
from 10 to 30 .mu.m were monodispersed, and had a small
flattening.
<Evaluation of the Emission Excitation Spectrum>
[0107] FIG. 2 indicates an emission excitation spectrum of the
obtained phosphor. In addition, in the following Table 1, the
composition, emission peak wavelength, relative luminance with
respect to YAG:Ce, absorbing ratio, external quantum efficiency,
internal quantum efficiency, and ratio of the emission peak
intensity excited at a wavelength by which the maximum excitation
intensity is obtained (I.sub.max) and the emission peak intensity
at an excitation wavelength of 550 nm (I.sub.ex550 nm)
((I.sub.ex550 nm)/(I.sub.max)) of the phosphor are indicated.
[0108] As indicated in FIG. 2 and Table 1, because the emission
peak wavelength of the obtained phosphor is 614 nm, and moreover
the light emission luminance is so very high as to be 1.22 in terms
of the ratio with respect to YAG:Ce, it has been found that the
phosphor is favorably usable as a red phosphor. In addition, in
view of the excitation spectrum, as compared to the excitation
spectrum of a conventional CASN or SCASN (see FIG. 1), because the
excitation intensity at around 550 nm is lower, and the ratio
represented by (I.sub.ex550 nm)/(I.sub.max) is so very small as to
be 0.17, it may be confirmed that the phosphor has such an
excitation spectrum shape that the influence by the multistage
excitation hardly appears.
<Evaluation of the Particle Shape>
[0109] In addition, from the result of the particle size
distribution measurement of the obtained phosphor, the circularity
was 85.9%. In addition, FIG. 3 shows electron microscopy (SEM)
images of the phosphor powder. Also from the SEM images, it is
found that the obtained particles are nearly monodispersed and
spherical having a diameter of around 20 .mu.m.
[0110] Note that, as described above, it has been found that the
phosphor may be inexpensively and easily produced without
subjecting a complicated producing step, and without requiring a
special producing facility, like a conventional nitride phosphor or
the like.
Example 2
<Preparation of the Phosphor>
[0111] Except that the composition for preparation is a composition
(Ca.sub.0.85Sr.sub.0.85Eu.sub.0.30SiO.sub.4), the phosphor was
prepared in the same way as described in Example 1. The finally
obtained phosphor was analyzed and found to have a composition of
Ca.sub.0.830Sr.sub.0.816Ba.sub.0.077Eu.sub.0.277Si.sub.0.968O.sub.3.936.
From the composition formula, it is supposed that a part of Ca and
Sr was substituted with Ba derived from BaCl.sub.2 added as a
flux.
<Evaluation of the Emission Excitation Spectrum>
[0112] FIG. 2 indicates an emission excitation spectrum of the
obtained phosphor. In addition, in the following Table 1, the same
evaluation results as those of Example 1 are indicated.
[0113] As indicated in FIG. 2 and Table 1, because the emission
peak wavelength of the obtained phosphor is 623 nm, and moreover
the light emission luminance is so very high as to be 1.16 in terms
of the ratio with respect to YAG:Ce, it has been found that the
phosphor is favorably usable as a red phosphor. In addition, in
view of the excitation spectrum, as compared to the excitation
spectrum of a conventional CASN or SCASN (see FIG. 1), because the
excitation intensity at around 550 nm is lower, and the ratio
represented by (I.sub.ex550 nm)/(I.sub.max) is so very small as to
be 0.22, it may be confirmed that the phosphor has such an
excitation spectrum shape that the influence by the multistage
excitation hardly appears.
<Evaluation of the Particle Shape>
[0114] In addition, from the result of the particle size
distribution measurement of the obtained phosphor, the circularity
was 88.9%. In addition, as the result of observation by an electron
microscope, similarly to FIG. 3, it has been found that the
obtained particles are nearly monodispersed and spherical having a
diameter of around 20 .mu.m.
Example 3
<Preparation of the Phosphor>
[0115] Except that the composition for preparation is a composition
(Ca.sub.0.975Sr.sub.0.975Eu.sub.0.05SiO.sub.4), the phosphor was
prepared in the same way as described in Example 1. The finally
obtained phosphor was analyzed and found to have a composition of
Ca.sub.0.967Sr.sub.0.913Ba.sub.0.07Eu.sub.0.05SiO.sub.4. From the
composition formula, it is supposed that a part of Ca and Sr was
substituted with Ba derived from BaCl.sub.2 added as a flux.
<Evaluation of the Emission Excitation Spectrum>
[0116] FIG. 2 indicates an emission excitation spectrum of the
obtained phosphor. In addition, in the following Table 1, the same
evaluation results as those of Example 1 are indicated.
[0117] As indicated in FIG. 2 and Table 1, because the emission
peak wavelength of the obtained phosphor is 604 nm, and moreover
the light emission luminance is so very high as to be 1.21 in terms
of the ratio with respect to YAG:Ce, it has been found that the
phosphor is favorably usable as a red phosphor. In addition, in
view of the excitation spectrum, as compared to the excitation
spectrum of a conventional CASN or SCASN (see FIG. 1), because the
excitation intensity at around 550 nm is lower, and the ratio
represented by (I.sub.ex550 nm)/(I.sub.max) is so very small as to
be 0.10, it may be confirmed that the phosphor has such an
excitation spectrum shape that the influence by the multistage
excitation hardly appears.
<Evaluation of the Particle Shape>
[0118] In addition, from the result of the particle size
distribution measurement of the obtained phosphor, the circularity
was 87.8%. In addition, as the result of observation by an electron
microscope, similarly to FIG. 3, it has been found that the
obtained particles are nearly monodispersed and spherical having a
diameter of around 20 .mu.m.
Comparative Example 1
<Preparation of the Phosphor>
[0119] Except that, in the firing step, SrCl.sub.2 was used as a
flux and 20% by weight thereof with respect to the weight of the
calcined powder were added, followed by mixing, the phosphor was
obtained by performing the same operation as described in Example
1. The composition of the obtained phosphor was a composition of
the original raw material blending ratio
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4).
<Evaluation of the Emission Excitation Spectrum>
[0120] FIG. 4 indicates an emission excitation spectrum of the
obtained phosphor, as compared to Example 1. In addition, in the
following Table 1, the same evaluation results as those of the
Examples are indicated.
[0121] As indicated in FIG. 4 and Table 1, because the emission
peak wavelength is 615 nm in a longer wavelength side than 600 nm,
it has been found that the phosphor is usable as a red phosphor.
However, the emission intensity was so very low as to be 0.89 in
terms of the ratio with respect to conventional YAG:Ce.
<Evaluation of the Luminous Efficiency of the Phosphor>
[0122] In addition, although the absorbing ratio by the obtained
phosphor was so high as to be 86.8%, the internal quantum
efficiency and the external quantum efficiency were lower than
those of the Examples.
<Evaluation of the Particle Shape>
[0123] In addition, from the result of the particle size
distribution measurement of the obtained phosphor, the circularity
was 89.3%. In addition, the SEM image of the phosphor powder has
approximately the same shape as that of Example 1 shown in FIG. 3,
and thus it has been confirmed that the obtained particles are
nearly monodispersed and spherical having a diameter of around 20
.mu.m.
Comparative Example 2
<Preparation of the Phosphor>
[0124] Except that the composition for preparation was a
composition
(Ca.sub.0.875Sr.sub.0.875Ba.sub.0.10Eu.sub.0.15SiO.sub.4), the
phosphor was obtained by performing the same operation as described
in Example 1. The finally obtained phosphor was analyzed and found
to have a composition of
Ca.sub.0.878Sr.sub.0.827Ba.sub.0.155Eu.sub.0.14SiO.sub.4. From the
composition formula, it is supposed that a part of Ca and Sr was
substituted with Ba derived from BaCl.sub.2 added as a flux.
<Evaluation of the Emission Excitation Spectrum>
[0125] FIG. 4 indicates an emission excitation spectrum of the
obtained phosphor, as compared to Example 1. In addition, in the
following Table 1, the same evaluation results as those of Example
1 are indicated.
[0126] As indicated in FIG. 4 and Table 1, because the emission
peak wavelength is 607 nm in a longer wavelength side than 600 nm,
it has been found that the phosphor is usable as a red phosphor.
However, the emission intensity was so very low as to be 0.82 in
terms of the ratio with respect to conventional YAG:Ce.
<Evaluation of the Luminous Efficiency of the Phosphor>
[0127] In addition, the absorbing ratio by the obtained phosphor
was so slightly lower as to be 82.7% than those by the Examples,
and the internal quantum efficiency and the external quantum
efficiency were also very lower than those of the Examples.
<Evaluation of the Particle Shape>
[0128] In addition, from the result of the particle size
distribution measurement of the obtained phosphor, the circularity
was 89.3%. In addition, the SEM image of the phosphor powder has
approximately the same shape as that of Example 1 shown in FIG. 3,
and thus it has been confirmed that the obtained particles are
nearly monodispersed and spherical having a diameter of around 20
.mu.m.
Comparative Example 3
<Preparation of the Phosphor>
[0129] Except that, in the firing step, without the use of a flux,
the reduction firing were performed in a temperature condition of
from 1,400.degree. C. for 2 hours, the phosphor was obtained by
performing the same operation as described in Example 1. Note that
because a flux was not used, the remaining flux-removal process was
not performed. The composition of the obtained phosphor was a
composition of the original raw material blending ratio
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4).
<Evaluation of the Emission Excitation Spectrum>
[0130] In the following Table 1, the same evaluation results as
those of the Examples are indicated.
[0131] As indicated in Table 1, because the emission peak
wavelength is 615 nm in a longer wavelength side than 600 nm, it
has been found that the phosphor is usable as a red phosphor.
However, the emission intensity was so extremely low as to be 0.40
in terms of the ratio with respect to conventional YAG:Ce.
<Evaluation of the Luminous Efficiency of the Phosphor>
[0132] In addition, the absorbing ratio by the obtained phosphor
was so lower as to be 69.3% than those by the Examples, and the
internal quantum efficiency and the external quantum efficiency
were also very lower than those of the Examples, indicating that
the effectiveness was inferior.
<Evaluation of the Particle Shape>
[0133] In addition, it was clear that the obtained powder was
composed of aggregated particles of the order of from 2 to 3 .mu.m
having an extremely low circularity. This is because a flux as a
crystal grower was not used.
Comparative Example 4
<Preparation of the Phosphor>
[0134] In accordance with a method disclosed in Patent Literature 4
(JP 2008-24791 A), the phosphor having a composition represented by
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4) was prepared.
[0135] First of all, as raw materials, CaCO.sub.3 (made by Wako
Pure Chemical Industries, Ltd.), SrCO.sub.3 (made by Kanto Chemical
Co., Inc.), Eu.sub.2O.sub.3 (3N, made by Kojundo Chemical Lab. Co.,
Ltd.) and SiO.sub.2 (Admafine SO-E1, made by Admatechs Company
Limited) were used and weighted so as to have a composition formula
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4). Furthermore, 3% by
weight of NH.sub.4Cl were added thereto with respect to the base
powder, followed by uniformly mixing by a ball mill.
[0136] The mixed raw materials obtained were contained in a
container, and first of all, reduction fired under a reducing
atmosphere of N.sub.2--H.sub.2 at 1,200.degree. C. for 4 hours, so
that a primary fired product was obtained. This product was
pulverized, and the pulverized one was contained again in a
crucible, which was subsequently placed in a furnace. The inside of
the furnace was then replaced with a vacuum. Next, secondary firing
was performed under an atmosphere of N.sub.2-5% H.sub.2 at
1,200.degree. C. for 4 hours, so that a secondary fired product was
obtained. The obtained secondary fired product was pulverized in
water, followed by sieving and dehydrating by a suction filtration.
Finally, drying was performed in a dryer at 150.degree. C.,
followed by additional sieving, so that a phosphor was obtained.
The composition of the obtained phosphor was a composition of the
original raw material blending ratio
(Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4).
<Evaluation of the Emission Excitation Spectrum>
[0137] FIG. 4 indicates an emission excitation spectrum of the
obtained phosphor, as compared to Example 1. In addition, in the
following Table 1, the same evaluation results as those of the
Examples are indicated.
[0138] As indicated in FIG. 4 and Table 1, because the emission
peak wavelength is 617 nm in a longer wavelength side than 600 nm,
it has been found that the phosphor is usable as a red phosphor.
However, the emission intensity was so extremely low as to be 0.36
in terms of the ratio with respect to conventional YAG:Ce.
<Evaluation of the Luminous Efficiency of the Phosphor>
[0139] In addition, the absorbing ratio by the obtained phosphor
was so lower as to be 72.5% than those by the Examples, and the
internal quantum efficiency and the external quantum efficiency
were also very lower than those of the Examples, indicating that
the effectiveness was inferior.
<Evaluation of the Particle Shape>
[0140] In addition, FIG. 5 shows electron microscopy (SEM) images
of the phosphor particles. The obtained powder was composed of
aggregated particles of the order of from 2 to 3 .mu.m, as shown in
FIG. 5. In addition, from the SEM images, it is found that the
particles have an extremely low circularity.
TABLE-US-00001 TABLE 1 EMISSION RELA- ABSORB- INTERNAL EXTERNAL
PEAK WAVE- TIVE ING QUANTUM QUANTUM LENGTH LUMI- RATIO EFFCIEN-
EFFICIEN- Iex550/ CIRCU- COMPOSITION (nm) NANCE (%) CY (%) CY (%)
Imax LARITY EXAMPLE 1
Ca.sub.0.918Sr.sub.0.867Ba.sub.0.074Eu.sub.0141SiO.sub.4 614 1.22
85.0 65.5 55.7 0.17 85.9 EXAMPLE 2
Ca.sub.0.830Sr.sub.0.816Ba.sub.0.077Eu.sub.0.277Si.sub.0.968O.su-
b.3.936 623 1.16 89.6 58.5 52.4 0.22 88.9 EXAMPLE 3
Ca.sub.0967Sr.sub.0.913Ba.sub.0.07Eu.sub.0.05SiO.sub.4 604 1.21
84.1 65.2 54.9 0.10 87.8 COMPARATIVE
Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4 615 0.89 86.8 46.3
40.2 0.18 89.3 EXAMPLE 1 COMPARATIVE
Ca.sub.0.878Sr.sub.0.827Ba.sub.0.155Eu.sub.0.14SiO.sub.4 607 0.82
82.7 44.3 36.3 0.10 89.3 EXAMPLE 2 COMPARATIVE
Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4 615 0.40 69.3 24.4
16.9 0.10 AGGRE- EXAMPLE 3 GATED PARTI- CLES COMPARATIVE
Ca.sub.0.925Sr.sub.0.925Eu.sub.0.15SiO.sub.4 617 0.36 72.5 19.8
14.3 0.10 AGGRE- EXAMPLE 4 GATED PARTI- CLES
* * * * *